These investigations are to identify the involvement of transfer RNA in the regulation of amino acid biosynthesis and to determine the functions of tRNA modifications in this regulation. The following aspects are of interest: l. Mutants of Salmonella typhimurium isolated as having altered regulation of several amino acid biosynthetic pathways are being characterized to determine if the pleiotropic phenotypes are caused by lesions affecting tRNA maturation. These studies include assays of several biosynthetic enzymes to determine if the regulation of their synthesis has been altered and a number of biochemical analyses of purified tRNA from the mutants to detect any alterations in modified bases. 2. The regulation of enzyme synthesis is being examined for some previously unstudied amino acid biosynthetic pathways to determine if tRNA is involved in their control. This includes physiological experiments in which the various enzyme levels are monitored and mutant selections for strains having altered regulation. BIBLIOGRAPHIC REFERENCES: Brenchley, J. and L. Patil. 1976. Mutants of Salmonella typhimurium resistant to methionine sulfoximine. ASM Abstracts. p. 161. Jegede, V. and J. Brenchley. 1976. Thialysine resistant mutant of Salmonella typhimurium with an altered tRNA profile. ASM Abstracts. p. 143.